Method of producing reinforcements in electro-deposits



Nov. 3, 1970 c. H. ESOLA ET AL 3,537,960

METHOD OF PRODUCING REINFORCEMENTS IN ELECTRO-DEPOSITS Filed Dec. 6,1968 INVENTOR. CHARLES H. EsoLA,

DONALD 6. KRE/TZ, Ham/v Irv/(W AGENT United States Patent O 3,537,960METHOD OF PRODUCING REINFORCEMENTS IN ELECTRO-DEPOSITS Charles H. Esola,Springfield, and Donald B. Kreitz, Allentown, Pa., assignors to GeneralElectric Company, a corporation of New York Filed Dec. 6, 1968, Ser. No.781,862

Int. 01. C23b 5/48 U.S. Cl. 204-16 6 Claims ABSTRACT OF THE DISCLOSURECROSS-REFERENCE TO RELATED APPLICATION Ser. No. 718,925, filed Apr. 4,1968, by Charles H. Esola for Improvement in Electroplating.

BACKGROUND OF THE INVENTION Field of the invention This inventionpertains to the field of electroplating.

Description of the prior art The incorporation of solid inclusions inelectroplated coatings has been accomplished in the past by suspendingthe solids in the electroplating bath, usually by stirring the bath orotherwise maintaining a circulation of the bath to keep the solids insuspension. Alternatively, the substrate to be plated may be locatedwith its major surface approximately horizontal so that the solidsmerely lie by gravity upon the surface, and become included in thecourse of the plating process. The first method suffers from thedisadvantage that the same circulation which keeps the solids suspendedtends to carry them away from the substrate before they become attachedto it by the deposition of the plated coating, and the second method hasthe disadvantage that any foreign matter entering or formed (such assludge) in the bath will fall upon the substrate. The magnitude of thislatter disadvantage is indicated by the practice of electroplaters ingeneral of placing work to be plated upon supports which maintain itclear of the bottom of the plating tank.

SUMMARY OF THE INVENTION In the copending application of reference it istaught to prepare a substrate for electroplating with aluminum bycleaning the substrate with aqueous solutions, and then rinsing away theaqueous material with a solution of oleic acid in isopropyl alcohol.While still covered with the fatty acid solution, the substrate isimmersed in an aluminum plating bath which is a solution in organicsolvents, e.g., diethyl ether. The bath solvent dissolves away the fattyacid coating, permitting plating.

We have observed that the fatty acid solution coated upon the substrateis sufficiently sticky that reinforcing fibers such as fine silicafibers, needle-like crystals of alumina or spinel (known in the art aswhiskers), graphite fibers, or other insoluble material Which may forexample be of high tensile strength and thus valuable as a reinforcementwhen occluded, may be deposited upon the coated substrate and willadhere to it. A substrate so coated is then immersed in the platingbath, and a high Patented Nov. 3, 1970 current density is immediatelyapplied in order to produce an initial deposit as rapidly as possible,in order to tack the fibers to the substrate before the fatty acidcoating is completely removed by the plating bath solvents. Presumably,the coating is removed locally at points where deposition occurs, whilecoating remains at other points long enough to retain the fibers untilthe tacking operation is sufficiently advanced to hold the fibers. Whenthis stage has been reached, the current density may be adjusted tovalues appropriate to producing the desired deposition, and plating iscontinued until the requisite plating thickness has been produced. Thereinforcements are embedded in the plated coating.

Since the application of the inclusions to the adherently coatedsubstrate is a purely mechanical one, the particular orientation of thefibers may be controlled at will; their density at different parts ofthe surface may be varied arbitrarily up to the point where they are sodense as to preclude the contact of further additions with thesubstrate; mixed inclusions of differing densities may be appliedwithout danger of segregation such as would tend to occur in any processin which the inclusions were suspended in a circulating plating bath.Also (a point of importance if the inclusions are expensive, as some ofthe high-strength fibers tend to be) the utilization of the fibers isvery efficient; one is not left after the operation with a largequantity of unused fibers to be recovered from a spent bath. Since theefficiency of utilization is high, the proportion of fibers (or otherinclusions) actually included in the product is better controllable,since there is no need to add a large excess of material which willremain in the bath in a difiicultly predictable amount.

The objects we achieve are thus, in general, the provision of inclusionsin a plated deposit with high efficiency of utilization of the supply ofinclusions, with generally predetermined orientation of the inclusions,and generally predetermined density of the inclusion distribution.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents a substrateaccording to our invention, coated with fibers;

FIG. 2 represents a conventional plating arrangement in which thesubstrate is being plated; and

FIG. 3 represents partly cut away a plated product.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 represents a substrate 10which may conveniently be of aluminum or aluminum-base alloy. Substrate10 may be cleaned by conventional means'to remove grease or otherdeposits, and then rinsed with a solution of equal parts of water andconcentrated hydrochloric acid. This solution is in turn rinsed off witha solution of 60 percent by weight of oleic acid in isopropyl alcohol,the material adhering after the final rinse being allowed to dry in airuntil it becomes somewhat tacky from the evaporation of the alcohol.Alternatively, concentrated oleic acid may be applied without a solventand heated in an air circulating oven until it becomes somewhat viscous.Inclusions 12, which are represented as fibers since fiberreinforcedmetals have a known utility as light-weight structural materials, arethen applied to the tacky surface. This may be done, e.g., by shakingthem from a fiat scoop. If necessary, they may then be pressed to theadhesive coating by a clean flat spatula to insure their retention. Anyexcess or loose fibers are shaken off, and the substrate is immersed ina plating bath, as represented in FIG. 2.

FIG. 2 represents an enclosed Vessel 14, with cover 16 and a source ofinert gas 18 connected to provide an inert atmosphere over the bath 20,excess being vented through 21. Bath 20 may be an aluminum plating bathaccording to the teachings of Brenner et al. in US. Pat. 2,651,608. Ananode 22 and the support 24 for the substrate are represented connectedto a conventional plating current supply 26, represented simply by arectangle. Immediately upon immersion, a plating current of density fromabout 60 to 120 amperes per square foot is applied for O.25-1.0 minute.This high current density produces tacking of the fibers, and thecurrent density may then be reduced to a value better suited to build upthe deposit 28 to the desired thickness. During the plating process thebath 20 dissolves the oleic acid and any isopropyl alcohol stillretained by the oleic acid. Upon completion of the plating to thedesired thickness the substrate 10, hearing the deposit 28 with thefibers 12 embedded in it, is removed from the bath and washed to removethe bath residue and dried.

The same basic method may be used more readily in conventional aqueousbaths, since there are many water soluble adhesives which have long beenknown to be desirable addition agents for producing desirablyfine-grained electroplated deposits. Alexanders Colloid Chemistry, D.van Nostrand Company, at page 190 of the third edition, published in1929, mentions this fact, and cites specifically Mueller and Bahntje,Zeitschrift fuer Elektrochemie, 1906, vol. 12, page 317, for the factthat gelatin and egg albumin actually produce a slightly denserelectrodeposit of copper than occurs in the same plating bath in theirabsence. An adhesive coating of gelatine may be applied to the workpieceand used to retain inclusions applied to it during strike platingprecisely as in the previous example.

If it is desired to provide more than one layer of inclusions, a plateddeposit containing a first layer of inclusions, produced as abovedescribed, may itself be used as a substrate for repetition of theprocess by applying to another layer of inclusions and plating upon thatlayer. This process may be repeated as often as required to build up adeposit with as many layers of inclusions as required.

The plated deposit with its inclusions may be used as a deposit upon theoriginal substrate, or alternatively, it may be stripped from theoriginal substrate in accordance with the known art and itselfconstitute the product of the process, being a reinforced metal capableof high tensile strength.

What is claimed is:

1. The method of forming an electroplated deposit containing inclusionswhich comprises the steps of:

(a) applying to a metal substrate a coating of an adhesive materialwhich is soluble in an electroplating bath;

(b) depositing upon the substrate so coated a layer of inclusionmaterial to be included as inclusions in an electroplated deposit;

(c) immersing the said substrate in the said electroplating bath;

(d) immediately after the said immersion applying a high density ofplating current to the said substrate to affix the said inclusionmaterial to the said substrate by plating metal from the saidelectroplating bath upon the said substrate;

(e) adjusting the density of the plating current to a value suited tothe deposition of an electroplated deposit from the said electroplatingbath, and plating upon the said substrate and around the said inclusionmaterial an electroplated deposit.

2. The method claimed in claim 1 in which (a) the said adhesive materialcomprises a fatty acid;

(b) the said electroplating bath is a solution comprising an organicsolvent.

3. The method claimed in claim 2 in which the said fatty acid is oleicacid.

4. The method claimed in claim 2 in which the said organic solvent isdiethyl ether.

5. The method claimed in claim 2 in which the said electroplating bathis adapted to electroplate aluminum.

6. The method claimed in claim 5 dependent on claim 1, in which the highdensity of plating current recited in claim 1 has a value of at leastamperes per square foot and not greater than amperes per square foot.

References Cited UNITED STATES PATENTS 3,441,487 4/1969 Rea et al 20416FOREIGN PATENTS 602,099 7/ 1960' Canada.

1,048,934 11/1966 Great Britain.

ROBERT K.- MIHALEK, Primary Examiner T. TUFARIELLO, Assistant Examiner

